U.S. Pat. No. 7,330,457 describes a cooperative wireless communication network where a wireless source node (source) uses a relay node to forward data to a destination node (destination) if the relaying reduces delay. Otherwise, the traffic is sent directly from the source to the destination. Transmission rates on links between the source, relay and destination depend on channel conditions. However, that method is only applicable for wireless local area networks (LAN), and the decision of whether or not to use the relay is made at the source node.
U.S. Pat. No. 6,505,035 describes rate control in a wireless network. The transmission rate between a base station and each mobile station can be changed according to the channel state information, and reception quality. The mobile station can report the reception quality to the base station, and the base station switches the transmission rate accordingly. That method does not consider the use of relay nodes.
As shown in FIG. 1A, U.S. patent application Ser. No. 12/651,472, entitled, “Cooperative Relay Communication in Wireless OFDMA Star Networks,” filed Jan. 3, 2010, by Yim et al. describes a star network including N slave nodes (slaves) 101, and a master node 102 (master). The slaves can use orthogonal frequency division multiple access (OFDMA) and code division multiple access (CDMA) to concurrently transmit to and receive from the coordinator. The NC sub-carriers of the network are equally assigned so that each slave has is assigned NC/N sub-carriers. Typically the data are transmitted as packets.
As shown in FIG. 1B, a transmission interval between two beacons 105 broadcast by the master constitutes a superframe 110. The slaves are assigned to groups. For slaves in the same group, they have the same active interval 111, and inactive intervals 112. Slaves in different groups have different active and inactive intervals. The slaves transmit data concurrently to the master during their respective active interval after receiving the beacon, and the slaves are inactive during their respective inactive interval. That method assumes that all the slaves use the same modulation and coding scheme, regardless of the channel conditions between slaves and the master.
Clarification Note: Some slaves may have inactive period first, then active, then become inactive again. So for slaves in the same group, they have the same active interval (singular), and have either one or two inactive intervals.